give access to the original exception raised in case of a parse error

actionpack/lib/action_controller/metal/exceptions.rb

@@ -3,6 +3,13 @@ module ActionController
   end
 
   class BadRequest < ActionControllerError #:nodoc:
+    attr_reader :original_exception
+
+    def initialize(type, e)
+      super("Invalid #{type} parameters: #{e.message}")
+      @original_exception = e
+      set_backtrace e.backtrace
+    end
   end
 
   class RenderError < ActionControllerError #:nodoc:

actionpack/lib/action_dispatch/http/request.rb

@@ -253,7 +253,7 @@ module ActionDispatch
     def GET
       @env["action_dispatch.request.query_parameters"] ||= (normalize_parameters(super) || {})
     rescue TypeError => e
-      raise ActionController::BadRequest, "Invalid query parameters: #{e.message}", e.backtrace
+      raise ActionController::BadRequest.new(:query, e)
     end
     alias :query_parameters :GET
 
@@ -261,7 +261,7 @@ module ActionDispatch
     def POST
       @env["action_dispatch.request.request_parameters"] ||= (normalize_parameters(super) || {})
     rescue TypeError => e
-      raise ActionController::BadRequest, "Invalid request parameters: #{e.message}", e.backtrace
+      raise ActionController::BadRequest.new(:request, e)
     end
     alias :request_parameters :POST
 

actionpack/test/dispatch/request_test.rb

@@ -560,6 +560,20 @@ class RequestTest < ActiveSupport::TestCase
     assert_equal({}, request.parameters)
   end
 
+  test "we have access to the original exception" do
+    mock_rack_env = { "QUERY_STRING" => "x[y]=1&x[y][][w]=2", "rack.input" => "foo" }
+    request = nil
+    request = stub_request(mock_rack_env)
+
+    e = assert_raises(ActionController::BadRequest) do
+      # rack will raise a TypeError when parsing this query string
+      request.parameters
+    end
+
+    assert e.original_exception
+    assert_equal e.original_exception.backtrace, e.backtrace
+  end
+
   test "formats with accept header" do
     request = stub_request 'HTTP_ACCEPT' => 'text/html'
     request.expects(:parameters).at_least_once.returns({})